The present invention relates to an arrangement for determining the relative angular orientation between a first machine element and a second machine element and, more particularly, to an arrangement for determining the relative angular orientation of an excavator bucket with respect to the dipper stick of the excavator.
Control systems have been developed for monitoring and automatically controlling the operation of various types of construction equipment, such as for example excavators. Such systems of this general type are disclosed in U.S. Pat. No. 5,461,803, issued Oct. 31, 1995, to Rocke; U.S. Pat. No. 5,062,264, issued Nov. 5, 1991, to Frenette et al; and U.S. Pat. No. 4,964,779, issued Oct. 23, 1990, to Sagaser. In each of these patents, a positioning and control system is disclosed that includes an arrangement for measuring the relative positions of various machine elements, comparing the measured positions with the desired positions in a feedback control system, and adjusting the machine element positions accordingly. In the Rocke patent, displacement sensors sense the amount of piston extension in the boom, dipper stick, and bucket hydraulic actuators. To accomplish this, a radio frequency sensor is provided inside each of the hydraulic cylinders. The sensor includes a pair of loop antennas that transmit and receive radio frequency electromagnetic signals, exciting a transverse electromagnetic field in the cavity when the frequency of the signal corresponds to the resonant frequency of the cavity. The resonant frequency of the cavity is primarily dependent upon the longitudinal length of the cavity. Therefore, a voltage controlled oscillator acts under the control of a sawtooth voltage waveform from a function generator to deliver a variable frequency signal to the first loop antenna. An RF detector monitors the second loop antenna for an indication that the resonant frequency has been reached. At resonance, a microprocessor samples the output of the voltage-controlled oscillator and correlates the resonant frequency to the length of the coaxial cavity.
The Frenette patent suggests that angle encoders at the pivot points between machine elements may be used to measure the relative positions of these machine elements. Alternatively, the Frenette patent suggests that a sensor measuring the displacement of an actuator, or a camera recording the location of the machine elements may be used. Finally, the Sagaser patent discloses the use of a special hydraulic actuator that includes a specially constructed potentiometer arrangement inside the actuator that varies in electrical resistance in relation to the extension of the piston.
These arrangements are expensive, require special parts, and may require frequent service adjustments. Further, the length of time required for servicing such arrangements may be longer than is desirable, due to the need to disassemble the actuators or other components. Accordingly, it is seen that there is a need for a simple, rugged, reliable, and economical arrangement for determining the relative angular orientation between a first machine element and a second machine element.